/*
 * ThreadPool.h
 *
 * open source  From:https://github.com/progschj/ThreadPool
 */

#ifndef COMMON_SOURCE_CPP_THREADPOOL_HPP_
#define COMMON_SOURCE_CPP_THREADPOOL_HPP_

#include <vector>
#include <queue>
#include <memory>
#include <thread>
#include <mutex>
#include <chrono>
#include <condition_variable>
#include <future>
#include <functional>
#include <stdexcept>
namespace gdface{
class ThreadPool {
public:
    const size_t concurrency;
    // if true,ignore if work queue is empty, force detach work thread while 'stop' is set, 
    // otherwise after finishing all task in work queue ,and detach.
    bool force;
    ThreadPool(size_t concurrency,bool force = false) : concurrency(concurrency), stop(false)
    {
        for (size_t i = 0; i < this->concurrency; ++i)
            workers.emplace_back(
                [this]
                {
                    for (;;)
                    {
                        std::function<void()> task;

                        {
                            std::unique_lock<std::mutex> lock(this->queue_mutex);
                            this->condition.wait_for(lock, std::chrono::milliseconds(100),
                                [this] { return this->stop || !this->tasks.empty(); });
                            if (this->stop)
                            {
                                if (this->force)
                                    return;
                                else if(this->tasks.empty())
                                    return;
                            }else if (this->tasks.empty())
                                continue;
                            task = std::move(this->tasks.front());
                            this->tasks.pop();
                        }
                        try
                        {
                            task();
                        }
                        catch (const std::exception&)
                        {
                            // DO NOTHING
                        }
                    }
                }
            );
    }

    // add new work item to the pool
    template<class F, class... Args>
    auto enqueue(F&& f, Args&&... args)
        -> std::future<typename std::result_of<F(Args...)>::type>{
        using return_type = typename std::result_of<F(Args...)>::type;

        auto task = std::make_shared< std::packaged_task<return_type()> >(
                std::bind(std::forward<F>(f), std::forward<Args>(args)...)
            );

        std::future<return_type> res = task->get_future();
        {
            std::unique_lock<std::mutex> lock(queue_mutex);

            // don't allow enqueueing after stopping the pool
            if(stop)
                throw std::runtime_error("enqueue on stopped ThreadPool");

            tasks.emplace([task](){ (*task)(); });
        }
        condition.notify_one();
        return res;
    }

    // the destructor joins all threads
    ~ThreadPool()
    {
        {
            std::unique_lock<std::mutex> lock(queue_mutex);
            stop = true;
        }
        // remove,because the code will cause deadlock while dynamic library unload
        //condition.notify_all();
        for (std::thread &worker : workers)
            worker.join();
    }

private:
    // need to keep track of threads so we can join them
    std::vector< std::thread > workers;
    // the task queue
    std::queue< std::function<void()> > tasks;

    // synchronization
    std::mutex queue_mutex;
    std::condition_variable condition;
    bool stop;
};


} /* namespace gdface */

#endif /* COMMON_SOURCE_CPP_THREADPOOL_HPP_ */
